APD forces power to come from an external adapter connected from VDD1 to RTN by opening the hotswap switch, disabling the CLS output (see PPD pin description), and enabling the T2P output. TI recommends a resistor divider on APD when it is connected to an external adapter. The divider provides ESD protection, leakage discharge for the adapter ORing diode, and input voltage qualification. Voltage qualification assures the adapter output voltage is high enough that it can support the PD before the PoE current is cut off.
Select the APD divider resistors per Equation 1 where VADPTR-ON is the desired adapter voltage that enables the APD function as adapter voltage rises.
Place the APD pulldown resistor adjacent to the APD pin.
APD should be tied to ARTN when not used.